Thermoplastic elastomer compositions rheology-modified using peroxides and free radical coagents

ABSTRACT

Rheology-modified thermoplastic elastomer compositions comprising a melt blend of an ethylene/a-olefin polymer and a high melting polymer such as polypropylene or a propylene/a-olefin copolymer wherein the rheology modification is induced by a combination of a peroxide and a free radical coagent. The resulting compositions have an elastomeric phase, a non-elastomeric phase and certain physical properties that exceed those of a like composition that is rheology-modified by peroxide alone. The compositions can be used to make a variety of articles of manufacture, such as automotive instrument panel skins, via calendaring and thermoforming procedures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/234,599 filed Sep. 22, 2000.

FIELD OF THE INVENTION

This invention relates generally to rheology-modified thermoplasticelastomer (TPE) compositions that comprise an elastomeric ethylene/alpha(α)-olefin (EAO) polymer or EAO polymer blend and a high meltingpropylene polymer, wherein both components are peroxide-modified and tothe preparation of the compositions, use of such compositions inprocesses such as calendaring and thermoforming to make articles ofmanufacture and the resulting articles of manufacture. This inventionparticularly relates to such compositions wherein the rheologymodification is induced by a combination comprising an organic peroxideand a free radical coagent, methods for preparing the compositions, suchas by modifying a physical blend of the components, and use of suchcompositions in calendaring operations and thermoforming applications.

BACKGROUND OF THE INVENTION

Heck et al. describe rheology modified TPE compositions in WO 98/32795.The rheology modification can be induced by various means includingperoxides and radiation. The compositions of Heck et al. are said toexhibit a combination of four properties: shear thinning index (STI),melt strength (MS), solidification temperature (ST) and upper servicetemperature (UST). While these compositions are useful in applicationssuch as automotive parts and boot shafts, improved compositions areneeded for calendaring operations and thermoforming applications.

Compositions having a high melt toughness are desired in calendaringoperations. Melt toughness, as used herein, is the product of the meltstrength and the melt extensibility. In many instances, the calendarrolls are fed with a composition in the form of a molten rod. Thismolten composition must be able to spread across the calendar rolls. TheHeck et al. compositions only spread partially across the calendarrolls.

Compositions having a high melt toughness also are preferred forthermoforming applications. In addition, tensile properties of thecompositions at elevated temperatures are important for theseapplications. For example, one method of manufacturing instrument panelskin material is to either calender or extrude embossed sheeting. Thesheeting is then vacuum thermoformed to the contour of the instrumentpanel. One method to determine compound thermoformability is byevaluating its elevated stress-strain behavior. Often, flexiblepolypropylene thermoplastic (TPO) sheets are thermoformed attemperatures below the melting point of the polypropylene phase.Although the thermoforming process is one of biaxial extension, tensiletests at the thermoforming temperatures can be used to comparethermoforming and grain retention behavior. The peaks and valleys of theembossed grain are areas of greater and lesser thickness and a look atthe grain shows that the valleys are narrower and less glossy than thepeak areas. When a skin is thermoformed, the thinner areas will besubject to greater stress and the greater applied stress in these areasconcentrates the elongation in the thinner valley areas. These areaselongate preferentially and the attractive “narrow valley, broad peak”appearance is lost, called “grain washout”—unless the material can bedesigned to elongate more evenly. Strain hardening is the property bywhich areas of material which have already been strained become stiffer,transferring subsequent elongation into areas which are as yetunstrained. Strain hardening thus allows a thermoformed skin to exhibitmore evenly distributed elongation and minimized grain washout.

One classic way to examine the strain hardening behavior of a materialis the Considère construction, by which the true stress, defined as theforce across the instantaneous cross sectional area is plotted againstthe draw ratio. Regular stress-strain graphs calculate the strain usingthe initial cross-sectional area, but the cross sectional areadiminishes as the sample is strained. The Considère construction isoften used to evaluate cold-drawing phenomena.

The Considère construction can be determined by the following equation:σ_(T)=σ(1+ε)where: σ_(T)=true stress

-   -   σ=engineering stress    -   ε=draw ratio=(L−Li)/Li        where: L=sample length under deformation    -   Li=initial sample length

The thermoformable compound must also exhibit acceptable elongationcharacteristics at elevated temperature. If the elongation is too low,the sheeting will tear when thermoformed. Thus, two particularlysignificant tensile properties are true ultimate tensile strength at140° C. and elongation to break at 140° C. Under extreme draw conditionsof some thermoforming applications, the Heck et al. compositions formholes leading to part failure.

Compositions having greater melt extensibility can be produced bylowering the level of peroxide used for rheology modification. However,lower peroxide levels result in lower melt strength and less tensilestrength. Thus, there is a need to produce rheology-modified TPEcompositions having an improved melt toughness. Further there is a needto enhance the high temperature tensile properties of such compositionsfor thermoforming applications.

SUMMARY OF THE INVENTION

Applicant has found that rheology modification by addition of at leastone peroxide and at least one free radical coagent has a signicanteffect on the melt toughness and high temperature tensile properties ofblends of at least one elastomeric EAO polymer or EAO polymer blend anda polyolefin such as PP. The rheology modified compositions of thisinvention have melt toughness and high temperature tensile propertiesthat are higher than corresponding compositions rheology modified by theaddition of peroxides alone. As such, one aspect of this invention is arheology-modified, substantially gel-free thermoplastic elastomer (TPE)composition comprising an EAO polymer or EAO polymer blend and a highmelting polymer selected from the group consisting of polypropylenehomopolymers and propylene/ethylene copolymers, wherein the compositionis rheology modified by at least one peroxide and at least one freeradical coagent and the rheology modified composition has a melttoughness of at least 600 centinewton millimeters per second (cNmm/s), atrue ultimate tensile strength at 140° C. of at least 3 mega-Pascals(MPa) and an elongation to break at 140° C. of at least 400%. The TPEcompositions may be compounded with conventional additives or processaids including, for example, fillers, stabilizers, dispersants, pigmentsand process oils. Compounds prepared from the rheology modified polymersof this invention retain their processing advantages over compoundsprepared from the same polymers, but rheology modified by peroxidealone.

A second aspect of this invention is a process for preparing arheology-modified, substantially gel-free TPE composition, the processcomprising: a) adding at least one peroxide and at least one freeradical coagent to a molten polymer blend that comprises an elastomericethylene/alpha-olefin polymer and a high melting polymer selected fromthe group consisting of polypropylene homopolymers andpropylene/ethylene copolymers; and b) maintaining the polymer blend in amolten state while subjecting it to conditions of shear sufficient todisperse the peroxide and coagent throughout the molten polymer blend,effect rheology modification of the polymers and substantially precludeformation of insoluble polymer gels, sufficient rheology modificationbeing measured by a melt toughness of at least 600 centinewtonmillimeters per second (cNmm/s), a true ultimate tensile strength at140° C. of at least 3 mega-Pascals (MPa) and an elongation to break at140° C. of at least 400%. The process optionally includes a step c)wherein the rheology modified polymer blend is converted to an articleof manufacture, preferably without intermediate steps of recovering therheology modified polymer blend as a solid and then converting the solidto a melt state sufficient for fabricating the article of manufacture.If desired, however, the process optionally includes the intermediatesteps.

One variation of the second aspect is a process for preparing arheology-modified, substantially gel-free TPE composition, the processcomprising: a) adding at least one peroxide and at least one freeradical coagent to at least one component of a polymer blend thatcomprises an elastomeric ethylene/alpha-olefin polymer and a highmelting polymer selected from the group consisting of polypropylenehomopolymers and propylene/ethylene copolymers; and b) converting thepolymer blend to a molten polymer blend while subjecting the blend toconditions of shear sufficient to disperse the peroxide and coagentthroughout the molten polymer blend, effect rheology modification of thepolymers and substantially preclude formation of insoluble polymer gels,sufficient rheology modification being measured by a melt toughness ofat least 600 centinewton millimeters per second (cNmm/s), a trueultimate tensile strength at 140° C. of at least 3 mega-Pascals (MPa)and an elongation to break at 140° C. of at least 400%. The processoptionally includes a sequential step c) wherein the rheology modifiedpolymer blend is converted to an article of manufacture, preferablywithout intermediate steps of recovering the rheology modified polymerblend as a solid and then converting the solid to a melt statesufficient for fabricating the article of manufacture. If desired,however, the process optionally includes the intermediate steps.

A second variation of the second aspect is a process for preparing arheology-modified, substantially gel-free thermoplastic elastomerarticle of manufacture, the process comprising: a) adding at least oneperoxide and at least one free radical coagent to a molten elastomericethylene/alpha-olefin polymer or elastomeric ethylene/alpha-olefinpolymer blend to provide a rheology-modified ethylene/alpha-olefinpolymer or ethylene/alpha-olefin polymer blend; b) adding to therheology-modified polymer or polymer blend a high melting polymerselected from the group consisting of polypropylene homopolymers andpropylene/ethylene copolymers to form a composite polymer blend; and c)converting the composite polymer blend into the article of manufacture,the article of manufacture having a melt toughness of at least 600centinewton millimeters per second (cNmm/s), an true ultimate tensilestrength at 140° C. of at least 3 mega-Pascals (MPa) and an elongationto break at 140° C. of at least 400%.

A third aspect of this invention is an article of manufacture having atleast one component thereof fabricated from the TPE composition of thefirst aspect of the invention. The TPE compositions suitably include atleast one additive selected from the group consisting of process oils,fillers and blowing agents. The compositions readily allow formation ofarticles of manufacture using apparatus for calendaring and/orthermoforming. In a related aspect, the TPE compositions of the firstaspect may be blended with another polymer, preferably one of thepolymers used to make the TPE composition, prior to fabrication of anarticle of manufacture. Such blending may occur by any of a variety ofconventional techniques, one of which is dry blending of pellets of theTPE composition with pellets of another polymer.

DESCRIPTION OF PREFERRED EMBODIMENTS

The rheology-modified compositions of this invention comprise anelastomeric EAO polymer or EAO polymer blend and a high melting polymer.The compositions desirably contain the EAO polymer or EAO polymer blendin an amount of from about 50 to about 90 wt % and the high meltingpolymer(s) in an amount of from about 50 to about 10 wt %, bothpercentages being based on composition weight. The amounts arepreferably from about 65 to about 85 wt % EAO and from about 35 to about15 wt % high melting polymer. The amounts are chosen to total 100 wt %polymer.

EAO polymers (also referred to as “ethylene polymers”) that are suitablefor this invention include interpolymers and diene modifiedinterpolymers. Illustrative polymers include ethylene/propylene (EP)copolymers, ethylene/butylene (EB) copolymers, ethylene/octene (EO)copolymers and ethylene/propylene/diene modified (EPDM) interpolymers.More specific examples include ultra low linear density polyethylene(ULDPE) (e.g., Attane™ made by The Dow Chemical Company), homogeneouslybranched, linear EAO copolymers (e.g. Tafmer™ by Mitsui PetroChemicalsCompany Limited and Exact™ by Exxon Chemical Company), and homogeneouslybranched, substantially linear EAO polymers (e.g. the Affinity™ polymersavailable from The Dow Chemical Company and Engage® polymers availablefrom DuPont Dow Elastomers L.L.C. The more preferred EAO polymers arethe homogeneously branched linear and substantially linear ethylenecopolymers with a density (measured in accordance with ASTM D-792) offrom about 0.85 to about 0.92 g/cm³, especially from about 0.85 to about0.90 g/cm³ and a melt index or 12 (measured in accordance with ASTMD-1238 (190° C./2.16 kg weight) of from about 0.01 to about 30,preferably 0.05 to 10 g/10 min.

The substantially linear ethylene copolymers or interpolymers (alsoknown as “SLEPs”) are especially preferred. In addition, the variousfunctionalized ethylene copolymers such as EVA (containing from about0.5 to about 50 wt % units derived from vinyl acetate) are alsosuitable. When using an EVA polymer, those that have an I₂ of from about0.01 to about 500, preferably 0.05 to 50 g/10 min are preferred.

“Substantially linear” means that a polymer has a backbone substitutedwith from 0.01 to 3 long-chain branches per 1000 carbons in thebackbone.

“Long-chain branching” or “LCB” means a chain length that exceeds thatof the alpha-olefin component of the EAO polymer or EAO polymer blends.Although carbon-13 nuclear magnetic resonance (C-13 NMR) spectroscopycannot distinguish or determine an actual number of carbon atoms in thechain if the length is greater than six carbon atoms, the presence ofLCB can be determined, or at least estimated, from molecular weightdistribution of the EAO polymer(s). It can also be determined from amelt flow ratio (MFR) or ratio (I₁₀/I₂) of melt index (I₁₀) via ASTMD-1238 (190° C., 10 kg weight) to I₂.

“Interpolymer” refers to a-polymer having polymerized therein at leasttwo monomers. It includes, for example, copolymers, terpolymers andtetrapolymers. It particularly includes a polymer prepared bypolymerizing ethylene with at least one comonomer, typically an α-olefinof 3 to 20 carbon atoms (C₃-C₂₀). Illustrative α-olefins includepropylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octeneand styrene. The α-olefin is desirably a C₃-C₁₀ α-olefin. Preferredcopolymers include EP, EB, ethylene/hexene-1 (EH) and EO polymers.Illustrative terpolymers include an ethylene/propylene/octene terpolymeras well as terpolymers of ethylene, a C₃-C₂₀ α-olefin and a diene suchas dicyclopentadiene, 1,4-hexadiene, piperylene or5-ethylidene-2-norbornene.

“Elastomeric”, as used herein, means an EAO polymer or EAO polymer blendthat has a density that is beneficially less than about 0.920 g/cc,desirably less than about 0.900 g/cc, preferably less than about 0.895g/cc, more preferably less than about 0.880 g/cc, still more preferablyless than about 0.875 g/cc, even more preferably less than about 0.870g/cc and a percent crystallinity of less than about 33%, preferably lessthan about 29% and more preferably less than about 23%. The density ispreferably greater than about 0.850 g/cc. Percent crystallinity isdetermined by differential scanning calorimetry (DSC).

SLEPs are characterized by narrow molecular weight distribution (MWD)and narrow short chain branching distribution (SCBD) and may be preparedas described in U.S. Pat. Nos. (USP) 5,272,236 and 5,278,272, relevantportions of both being incorporated herein by reference. The SLEPsexhibit outstanding physical properties by virtue of their narrow MWDand narrow SCBD coupled with long chain branching (LCB).

U.S. Pat. No. 5,272,236 (column 5, line 67 through column 6, line 28)describes SLEP production via a continuous controlled polymerizationprocess using at least one reactor, but allows for multiple reactors, ata polymerization temperature and pressure sufficient to produce a SLEPhaving desired properties. Polymerization preferably occurs via asolution polymerization process at a temperature of from 20° C. to 250°C., using constrained geometry catalyst technology. Suitable constrainedgeometry catalysts are disclosed at column 6, line 29 through column 13,line 50 of U.S. Pat. No. 5,272,236.

A preferred SLEP has a number of distinct characteristics, one of whichis an ethylene content that is between 20 and 90 wt %, more preferablybetween 30 and 89 wt %, with the balance comprising one or morecomonomers. The ethylene and comonomer contents are based on SLEP weightand selected to attain a total monomer content of 100 wt %. For chainlengths up to six carbon atoms, SLEP comonomer content can be measuredusing C-13 NMR spectroscopy.

Additional distinct SLEP characteristics include I₂ and MFR or I₁₀/I₂.The interpolymers desirably have an I₂ of 0.01-30 g/10 min, morepreferably from 0.05-10 g/10 min. The SLEP also has a I₁₀/I₂ (ASTMD-1238)≧5.63, preferably from 6.5 to 15, more preferably from 7 to 10.For a SLEP, the I₁₀/I₂ ratio serves as an indication of the degree ofLCB such that a larger I₁₀/I₂ ratio equates to a higher degree of LCB inthe polymer.

SLEPs that meet the aforementioned criteria include, for example,Engage® polyolefin elastomers and other polymers produced viaconstrained geometry catalysis by The Dow Chemical Company and DuPontDow Elastomers L.L.C.

The high melting polymer component of the TPEs of this invention is ahomopolymer of propylene or a copolymer of propylene with an α-olefinsuch as ethylene, 1-butene, 1-hexene or 4-methyl-1-pentene or a blend ofa homopolymer and a copolymer. Each of the homopolymer, the copolymer orthe blend of a homopolymer and a copolymer may be nucleated. Theα-olefin is preferably ethylene. The copolymer may be a random copolymeror a block copolymer or a blend of a random copolymer and a blockcopolymer. As such, this component is preferably selected from the groupconsisting of polypropylene (PP) homopolymers and propylene/ethylenecopolymers. This component has a MFR (230° C. and 2.16 kg weight) of 0.3to 60 g/10 min, preferably 0.8 to 40 g/10 min and more preferably 1 to35 g/10 min.

As used herein, “nucleated” refers to a polymer that has been modifiedby addition of a nucleating agent such as Millad™, a dibenzyl sorbitolcommercially available from Milliken. Other conventional nucleatingagents may also be used.

Preparation of polypropylene (PP) also involves the use of Zieglercatalysts such as a titanium trichloride in combination with aluminumdiethylmonochloride, as described by Cecchin, U.S. Pat. No. 4,177,160.Polymerization processes used to produce PP include the slurry process,which is run at about 50-90° C. and 0.5-1.5 MPa (5-15 atm), and both thegas-phase and liquid-monomer processes in which extra care must be givento the removal of amorphous polymer. Ethylene may be added to thereaction to form a polypropylene with ethylene blocks. PP resins mayalso be prepared by using any of a variety of metallocene, single siteand constrained geometry catalysts together with their associatedprocesses.

The peroxide is preferably an organic peroxide. Suitable organicperoxides have a half life of at least one hour at 120° C. Illustrativeperoxides include a series of vulcanizing and polymerization agents thatcontain α,α′-bis(t-butylperoxy)-diisopropylbenzene and are availablefrom Hercules, Inc. under the trade designation VULCUP™, a series ofsuch agents that contain dicumyl peroxide and are available fromHercules, Inc. under the trade designation Di-cup™ as well as Lupersol™peroxides made by Elf Atochem, North America or Trigonox™ organicperoxides made by Akzo Nobel. The Lupersol™ peroxides include Lupersol™101 (2,5-dimethyl-2,5-di(t-butylperoxy)hexane), Lupersol™ 130(2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3) and Lupersol™575 (t-amylperoxy-2-ethylhexonate). Other suitable peroxides include2,5-dimethyl-2,5-di-(t-butyl peroxy)hexane, di-t-butylperoxide,di-(t-amyl)peroxide, 2,5-di(t-amyl peroxy)-2,5-dimethylhexane,2,5-di-(t-butylperoxy)-2,5-diphenylhexane,bis(alpha-methylbenzyl)peroxide, benzoyl peroxide, t-butyl perbenzoate,3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane andbis(t-butylperoxy)-diisopropylbenzene.

The peroxide is suitably present in an amount that is within a range offrom about 100 to about 10,000 parts by weight per million parts byweight of polymer. The range is desirably from about 500 to about 5,000,preferably from about 1,000 to about 3,000 parts by weight.

The free radical coagent is a monomer or low molecular weight polymerhaving two or more functional groups with high response to freeradicals. Typically, these functional groups are either methacrylate,allyl or vinyl. The free radical coagent enhances the rheologymodification of the peroxide by two mechanisms. Firstly, by peroxideinduced allylic hydrogen abstraction from the coagent, a lower energystate, longer lived free radical is created. This free radical can theninduce branching in the ethylene elastomer by hydrogen abstraction. Dueto the lower energy state of the free radical, (β-scissioning anddisproportionation of either the polypropylene or ethylene elastomerphase is less likely to occur. Secondly, the multifunctional coagent canact as a bridging group between the polymer chains.

Suitable free radical coagents for this application would includediallyl terephthalate, triallylcyanurate, triallylisocyanurate, 1,2polybutadiene, divinyl benzene, trimethylolpropane trimethacrylate,polyethylene glycol dimethacrylate, ethylene glycol dimethacrylate,pentaerythritol triacrylate,allyl methacrylate, N N′-m-phenylenebismaleimide, toluene bismaleimide-p-quinone dioxime, nitrobenzene,diphenylguanidine. Preferred coagents are triallylcyanurate, 1,2polybutadiene, divinyl benzene, and trimethyolpropane trimethacrylate.

The coagent is suitably present in an amount that is within the range offrom about 100 to about 10,000 parts per million by weight. The range isdesirably from about 500 to about 5,000 parts, preferrably from 1,000 to3,000 parts per million by weight.

The peroxide and free radical coagent can be added by any conventionalmeans. Illustrative procedures include imbibing it onto polymer pelletsprior to compounding, adding it to polymer pellets as the pellets entera compounding apparatus such as at the throat of an extruder, adding itto a polymer melt in a compounding apparatus such as a Haake, a Banburymixer, a Farrel continuous mixer or a Buss kneader or injecting it intoan extruder, at 100% active ingredients (i.e., neat) or optionally as adispersion or solution in an oil, such as a processing oil, at a pointwhere the extruder contents are molten. A preferred procedure isimbibing the peroxide and coagent into the polymer pellets prior tocompounding.

The peroxide and free radical coagent are used in amounts sufficient toprovide a melt toughness of at least 600 centinewton millimeters persecond (cNmm/s), a true ultimate tensile strength at 140° C. of at least3 mega-Pascals (MPa) and an elongation to break at 140° C. of at least400% without substantial gel formation. The ratio of coagent to peroxideis suitably within the range from about 1:10 to 10:1 based on wt. %. Amore preferred ratio range is from about 1:5 to 5:1 and the mostpreferred ratio range is from about 1:2 to about 2:1. The optimum ratioof coagent is dependent on the ethylene/□-olefin-polypropylene ratioused in the compounds. A suitable range of EAO/PP on a weight percentbasis is 80/20-40/60. The preferred range is 65/35-75/25 weight percent.

Melt toughness, as used herein, is the product of the melt strength andmelt extensibility. Melt strength (MS), as used herein, is a maximumtensile force measured on a molten filament of a polymer melt extrudedfrom a capillary rheometer die at a constant shear rate of 33 reciprocalseconds (sec-1) while the filament is being stretched by a pair of niprollers that are accelerating the filament at a rate of 0.24 centimetersper second per second (cm/sec²) from an initial speed of 1 cm/sec. Themolten filament is preferably generated by heating 10 grams (g) of apolymer that is packed into a barrel of an Instron capillary rheometer,equilibrating the polymer at 190° C. for five minutes and then extrudingthe polymer at a piston speed of 2.54 cm/minute (cm/min) through acapillary die with a diameter of 0.21 cm and a length of 4.19 cm. Thetensile force is preferably measured with a Goettfert Rheotens that islocated so that the nip rollers are 10 cm directly below a point atwhich the filament exits the capillary die. Melt extensibility (ME), asused herein, is the maximum speed of the nip rollers from the GoettfertRheotens needed to break the filament, measured in cm/sec.

The high temperature ultimate tensile strength or ultimate tensilestrength at 140° C., as used herein, is measured by cutting ISO 37 T2dumbbell bars from either the compression molded plaque or extrudedsheet. When testing extruded sheet, the bars are cut in the machinedirection. The cut bar is then placed in a tensile testing machinefitted with an environmental chamber heated to 140° C. The bar isallowed to equilibrate for 10 minutes, then is strained at a cross headspeed of 50 cm/min. The tensile strength and elongation to break arerecorded.

In order to detect the presence of, and where desirable, quantifyinsoluble gels in a polymer composition such as the rheology-modifiedcompositions of this invention, simply soak the composition in asuitable solvent such as refluxing xylene for 12 hours as described inASTM D 2765-90, method B. Any insoluble portion of the composition isthen isolated, dried and weighed, making suitable corrections based uponknowledge of the composition. For example, the weight of non-polymericcomponents that are soluble in the solvent is subtracted from theinitial weight and the weight of non-polymeric components that areinsoluble in the solvent is subtracted from both the initial and finalweight. The insoluble polymer recovered is reported as percent gelcontent. For purposes of this invention, “substantially gel-free” meansa percent gel content that is desirably less than about 10%, moredesirably less than about 8%, preferably less than about 5%, morepreferably less than about 3%, still more preferably less than about 2%,even more preferably less than about 0.5% and most preferably belowdetectable limits when using xylene as the solvent. For certain end useapplications where gels can be tolerated, the percent gel content can behigher.

The compositions of this invention may be compounded with any one ormore materials conventionally added to polymers. These materialsinclude, for example, EAOs that have not been rheology modified, processoils, plasticizers, specialty additives including stabilizers, fillers(both reinforcing and non-reinforcing) and pigments. These materials maybe compounded with compositions of this invention either before or aftersuch compositions are rheology modified. Skilled artisans can readilyselect any suitable combination of additives and additive amounts aswell as timing of compounding without undue experimentation.

Process oils are often used to reduce any one or more of viscosity,hardness, modulus and cost of a composition. The most common processoils have particular ASTM designations depending upon whether they areclassified as paraffinic, naphthenic or aromatic oils. An artisanskilled in the processing of elastomers in general and therheology-modified TPE compositions of this invention in particular willrecognize which type of oil will be most beneficial. The process oils,when used, are desirably present in an amount within a range of fromabout 0.5 to about 50 wt %, based on total composition weight. Certainlow to medium molecular weight ester plasticizers may also used toenhance low temperature performance. Examples of esters which may beused include isooctyltallate, isooctyloleate, n-butyltallate,n-butyloleate, butoxyethyloleate, dioctylsebacate, di2-ethylehexylsebacate, dioctylazelate, diisooctyldodecanedioate, alkylalkyletherdiester glutarate.

A variety of specialty additives may be advantageously used incompositions of this invention. The additives include antioxidants,surface tension modifiers, anti-block agents, lubricants, antimicrobialagents such as organometallics, isothtazolones, organosulfurs andmercaptans; antioxidants such as phenolics, secondary amines, phophitesand thioesters; antistatic agents such as quaternary ammonium compounds,amines, and ethoxylated, propoxylated or glycerol compounds; fillers andreinforcing agents such as carbon black, glass, metal carbonates such ascalcium carbonate, metal sulfates such as calcium sulfate, talc, clay orgraphite fibers; hydrolytic stabilizers; lubricants such as fatty acids,fatty alcohols, esters, fatty amides, metallic stearates, paraffinic andmicrocrystalline waxes, silicones and orthophosphoric acid esters; moldrelease agents such as fine-particle or powdered solids, soaps, waxes,silicones, polyglycols and complex esters such as trimethylolpropanetristearate or pentaerythritol tetrastearate; pigments, dyes andcolorants; plasticizers such as esters of dibasic acids (or theiranhydrides) with monohydric alcohols such as o-phthalates, adipates andbenzoates; heat stabilizers such as organotin mercaptides, an octylester of thioglycolic acid and a barium or cadmium carboxylate;ultraviolet light stabilizers used as a hindered amine, ano-hydroxy-phenylbenzotriazole, a 2-hydroxy,4-alkoxyenzophenone, asalicylate, a cynoacrylate, a nickel chelate and a benzylidene malonateand oxalanilide. A preferred hindered phenolic antioxidant is Irganox™1076 antioxidant, available from Ciba-Geigy Corp. Each of the aboveadditives, if used, typically does not exceed 45 wt %, based on totalcomposition weight, and are advantageously from about 0.001 to about 20wt %, preferably from about 0.01 to about 15 wt % and more preferablyfrom about 0.1 to about 10 wt %.

The rheology-modified TPE compositions of this invention may befabricated into parts, sheets or other form using any one of a number ofconventional procedures for processing TPEs. The compositions can alsobe formed, spun or drawn into films, fibers, multi-layer laminates orextruded sheets, or can be compounded with one or more organic orinorganic substances, on any machine suitable for such purposes. Thecompositions are particularly advantageous for high temperature TPEprocesses such as calendaring, extruding and thermoforming.

The TPE compositions of this invention have surprisingly improvedproperties relative to blends of an EAO copolymer and a high meltingpolymer such as PP that have been subjected to rheology modification byperoxide only. Rheology modification by way of peroxide and free radicalcoagent provides a combination of desirable and improved melt toughnessand high temperature tensile properties.

The compositions of this invention can be formed into a variety ofshaped articles using conventional polymer fabrication processes such asthose identified above. A partial, far from exhaustive, listing ofsuitable shaped articles includes automobile body parts such asinstrument panel skins, bumper fascia, body side moldings, exteriortrim, interior trim,weather stripping, air dams, air ducts, and wheelcovers, and non-automotive applications such as polymer films, polymersheets, tubing, trash cans, storage containers, lawn furniture strips orwebbing, lawn mower, garden hose, and other garden appliance parts,recreational vehicle parts, golf cart parts, utility cart parts andwater craft parts. The compositions can also be used in roofingapplications such as roofing membranes. The compositions can further beused in fabricating components of footwear such as a shaft for a boot,particularly an industrial work boot. A skilled artisan can readilyaugment this list without undue experimentation.

The following examples illustrate but do not, either explicitly or byimplication, limit the present invention. Unless otherwise stated, allparts and percentages are by weight, on a total weight basis. Examplesof the present invention are identified by Arabic numerals andcomparative examples are represented by letters of the alphabet.

EXAMPLES AND COMPARATIVE EXAMPLE

Nine compositions, eight representing this invention (Examples 1-8) andone being a comparison (Comparative Example A), were prepared from twodifferent EAO polymers using the following procedure. All ninecompositions were produced by tumble blending the ingredients together,allowing the peroxide and coagent to imbibe into the pellets, thenprocessing the blend into pellets on a Werner Pfliederer ZSK-30co-rotating twin screw extruder. The pelletized compounds were thenprocessed into sheeting on a 2 inch Killion single screw extruder fittedwith a 6 inch wide sheeting die. Sheeting 0.050 inch thick was producedand tested.

The EAO polymers used in the examples were: EAO-1, an ethylene/1 -octenecopolymer having an I₂ of 0.5 g/10 min and a nominal density of 0.863g/cc (Engage® 8180 polyolefin elastomer from DuPont Dow ElastomersL.L.C.); EAO-2, an experimental ethylene/1-octene copolymer having anominal Mooney viscosity of 47, a nominal density of 0.868 g/cc, anumber average molecular weight of about 80,000 and a molecular weightdistribution (MWD) of about 2.3, as measured by gel permeationchromatography (produced by DuPont Dow Elastomers L.L.C.); and EAO-3, anexperimental ethylene/1-butene copolymer having a nominal Mooneyviscosity of 45, a nominal density of 0.870 g/cc, a number averagemolecular weight (Mn) of about 78,000, and a molecular weightdistribution (MWD) of about 2.0 as measured by gel permeationchromatography (produced by DuPont Dow Elastomers L.L.C.).

The polypropylene (PP) used in the examples was a polypropylenehomopolymer having a melt flow of 0.8 (Profax PD-191 from Montell).

The peroxides used in the examples were:POX-1,2,5-dimethyl-2,5-di(t-butylperoxy)hexane (Lupersol 101 from ElfAtochem); and POX-2, di(t-amyl)peroxide (DTAP from Crompton Chemical).

The free radical coagents used in the examples were: FRC-1,trimethylolpropane trimethacrylate (SR-350 KD96 (75% SR-350 fromSartomer Company, Inc. on calcium silicate prepared by AkronDispersions)); FRC-2, trimethylolpropane trimethacrylate (100% SR-350from Sartomer Company,Inc.); FRC-3, triallyl cyanurate (TAC from CytecIndustries, Inc.); and FRC-4, 1,2-polybutadiene (Ricon 152D (68% Ricon152 from Sartomer Coporation on calcium silicate, prepared by AkronDispersions)). FRC-4 was warmed to about 30° C. to form a liquid priorto tumble blending.

Examples 1-2 and Comparative Example A

Table I summarizes data for the compositions of Examples 1-2 andComparative Example A. Table I identifies the EAO polymer, the peroxideand the free radical coagent (for Examples 1 and 2), and specifies thewt % of the ingredients. TABLE I Example EAO-1 PP POX-1 FRC-1 1 68.730.8 0.2 0.3 2 68.6 30.7 0.3 0.4 A 68.6 30.7 0.7 0

The properties of the compositions of the examples and comparativeexample were determined and are reported in Table II below.

A Goeffert Rheotens measured the melt strength (MS) and meltextensibility (ME) of a molten filament of a polymer melt extruded froma capillary rheometer die. Melt toughness (MT) is the product of the MSand the ME. A constant shear rate of 33 sec⁻¹ was maintained while thefilament was being stretched by a pair of nip rollers that wereaccelerating the filament at a rate of 0.24 cm/sec² from an initialspeed of 1 cm/sec. The nip rollers were fitted with strain gages tomeasure the stress response of the molten filament to strain. Elevatedtemperature (140° C.) stress strain was measured with a tensile testingmachine fitted with an environmental chamber heated to 140° C. The truestress (true ultimate tensile strength (TUTS)) was determined using theConsidere equation and the elongation to break (ultimate strain (US))was measured. Gel content of the composition was measured by extractingwith refluxing xylene for 12 hours as described in ASTM D 2765-90. TABLEII 140° C. 140° C. MS ME MT TUTS US Gel Example (cN) (mm/s) (cNmm/s)(Mpa) (%) (wt %) 1 10.58 115.6 1223 0.480 >1200 0.9 2 17.36 78.1 13560.905 523 0.6 A 7.55 75.3 569 0.457 344 1.0

The data presented in Table II illustrate several points. First,Examples 1 and 2 show significantly higher melt toughness thanComparative Example A. These results evidence that higher melt toughnessis obtained using a lower level of peroxide with a free radical coagent.Second, Examples 1 and 2 show greater tensile properties at the hightemperature of 140° C. Example 1 has a slightly higher true ultimatetensile strength and a significantly higher ultimate stress thanComparative Example A. Example 2 has nearly twice the true ultimatetensile strength and significantly higher ultimate stress thanComparative Example A. Similar results are expected with other EAOpolymers, propylene polymers, and rheology modifiers or modificationprocesses, all of which are disclosed above.

Examples 3-8

Using different EAO polymers, peroxides and/or free radical coagents,the procedure and apparatus of Examples 1-2 were used to prepare sixadditional compositions of the invention. Table III identifies the EAOpolymer, the peroxide and the free radical coagent, and specifies the wt% of the ingredients. TABLE III Ex. EAO-1 EAO-2 EAO-3 PP POX-1 POX-2FRC-2 FRC-3 FRC-4 3 69.79 0 0 29.91 0 0.15 0.15 0 0 4 69.79 0 0 29.910.15 0 0 0.15 0 5 0 69.79 0 29.91 0.15 0 0.15 0 0 6 0 69.79 0 29.91 0.050 0.05 0 0 7 0 0 69.79 29.91 0.15 0 0.15 0 0 8 69.7585 0 0 29.8965 0.150 0 0 0.195

Table IV The properties of the compositions of Examples 3-8 weredetermined in the same manner as described above for Examples 1-2 andComparative Example A. They are reported in Table IV below. 140° C. 140°C. MS ME MT TUTS US Gel Example (cN) (mm/s) (cNmm/s) (Mpa) (%) (wt %) 327 43 1161 5.25 1367 0.9 4 25 61 1525 5.09 1287 1.4 5 27 45.9 1239 4.261510 1.1 6 13 82.6 1074 7.71 1300 0.9 7 21 65.3 1371 11.7 1324 0.16 8 2155.4 1163 9.6 1364 0.30

Examples 3-8 show much higher melt toughness (1074-1525 cN-mm/s) thanComparative Example A (569 cN-mm/s). Further, Examples 3-8 show muchhigher true ultimate tensile strength at 140° C. and significantlyhigher ultimate strain at 140° C. than Comparative Example A. Similarresults are expected with other EAO polymers and blends of EAO polymers,PP polymers, peroxides, free radical coagents or procedures and amountsof the same, all of which are disclosed herein.

1. A rheology-modified, substantially gel-free thermoplastic elastomercomposition comprising at least one elastomeric ethylene/alpha-olefinpolymer or ethylene/alpha-olefin polymer blend and at least one highmelting polymer selected from the group consisting of polypropylenehomopolymers and propylene/ethylene copolymers, wherein the rheologymodification is induced by a combination comprising a peroxide and afree radical coagent and the composition has a melt toughness of atleast about 600 cNmm/s, a true ultimate tensile strength at 140° C. ofat least about 3 MPa and an elongation to break at 140° C. of leastabout 400%.
 2. The composition of claim 1 wherein the peroxide is anorganic peroxide.
 3. The composition of claim 2 wherein the organicperoxide is selected from the group consisting ofα,α′-bis(t-butylperoxy)-diisopropylbenzene, dicumyl peroxide,di-(t-amyl)peroxide,2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3,2,5-dimethyl-2,5-di(t-butylperoxy)hexane,2,5(t-amyl peroxy-2-ethylhexonate), 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane, di-t-butylperoxide, 2,5-di(t-amylperoxy)-2,5-dimethylhexane, 2,5-di-(t-butylperoxy)-2,5-diphenylhexane,bis(alpha-methylbenzyl)peroxide, t-butyl perbenzoate, benzoyl peroxide,3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane andbis(t-butylperoxy)-diisopropylbenzene.
 4. The composition of claim 1wherein the free radical coagent is selected from the group consistingof diallyl terephthalate, triallylcyanurate, triallylisocyanurate,1,2-polybutadiene, divinyl benzene, trimethylolpropane trimethacrylate,polyethylene glycol dimethacrylate, ethylene glycol dimethacrylate,pentaerythritol triacrylate, allyl methacrylate, N,N′-m-phenylenebismaleimide, toluene bismaleimide-p-quinone dioxime, nitrobenzene, anddiphenylguanidine.
 5. The composition of claim 4 wherein the freeradical coagent is selected from the group consisting oftriallylcyanurate, 1,2-polybutadiene, divinyl benzene, andtrimethylolpropane trimethacrylate.
 6. The composition of claim 1,wherein the ethylene/α-olefin polymer has polymerized therein at leastone α-olefin comonomer, the α-olefin containing from 3 to 20 carbonatoms.
 7. The composition of claim 6, wherein the α-olefin contains from3 to 10 carbon atoms.
 8. The composition of claim 1, wherein theethylene/α-olefin polymer is a diene-modified polymer, the diene beingselected from the group consisting of norbornadiene, dicyclopentadiene,1,4-hexadiene, piperylene or 5-ethylidene-2-norbornene and mixturesthereof.
 9. The composition of claim 1, wherein the high melting polymeris a nucleated polymer.
 10. The composition of claim 1, furthercomprising a process oil in an amount within a range of from greaterthan 0 to about 50 weight percent, based on total composition weight.11. The composition of claim 1 or claim 10, further comprising a fillerin an amount within a range of from about 0 to about 70 weight percent,based on total composition weight.
 12. The composition of claim 1 orclaim 10, further comprising a blowing agent in an amount within a rangeof from greater than 0 to about 10 weight percent, based on totalcomposition weight.
 13. The composition of claim 11, further comprisinga blowing agent in an amount within a range of from greater than 0 toabout 10 weight percent, based on total composition weight.
 14. Aprocess for preparing a rheology-modified, substantially gel-free TPEcomposition, the process comprising: a) adding at least one peroxide andat least one free radical coagent to a molten polymer blend thatcomprises an elastomeric ethylene/alpha-olefin polymer and a highmelting polymer selected from the group consisting of polypropylenehomopolymers and propylene/ethylene copolymers; and b) maintaining thepolymer blend in a molten state while subjecting it to conditions ofshear sufficient to disperse the peroxide and coagent throughout themolten polymer blend, effect rheology modification of the polymers andsubstantially preclude formation of insoluble polymer gels, sufficientrheology modification being measured by a melt toughness of at leastabout 600 cNmm/s, a true ultimate tensile strength at 140° C. of atleast about 3 MPa and an elongation to break at 140° C. of least about400%.
 15. A process for preparing a rheology-modified, substantiallygel-free TPE composition, the process comprising: a) adding at least oneperoxide and at least one free radical coagent to at least one componentof a polymer blend that comprises an elastomeric ethylene/alpha-olefinpolymer and a high melting polymer selected from the group consisting ofpolypropylene homopolymers and propylene/ethylene copolymers; and b)converting the polymer blend to a molten polymer blend while subjectingthe blend to conditions of shear sufficient to disperse the peroxide andcoagent throughout the molten polymer blend, effect rheologymodification of the polymers and substantially preclude formation ofinsoluble polymer gels, sufficient rheology modification being measuredby a melt toughness of at least about 600 cNmm/s, a true ultimatetensile strength at 140° C. of at least about 3 MPa and an elongation tobreak at 140° C. of least about 400%.
 16. A process for preparing arheology-modified, substantially gel-free thermoplastic elastomerarticle of manufacture, the process comprising: a) adding at least oneperoxide and at least one free radical coagent to a molten elastomericethylene/alpha-olefin polymer or elastomeric ethylene/alpha-olefinpolymer blend to provide a rheology-modified ethylene/alpha-olefinpolymer or ethylene/alpha-olefin polymer blend; b) adding to therheology-modified polymer or polymer blend a high melting polymerselected from the group consisting of polypropylene homopolymers andpropylene/ethylene copolymers to form a composite polymer blend; and c)converting the composite polymer blend into the article of manufacture,the article of manufacture having a melt toughness of at least about 600cNmm/s, a true ultimate tensile strength at 140° C. of at least about 3MPa and an elongation to break at 140° C. of least about 400%.
 17. Theprocess of any of claims 14-16, wherein the melt toughness of therheology-modified composition is at least 700 cNmm/s.
 18. The process ofclaim 17, wherein the melt toughness of the rheology-modifiedcomposition is at least 800 cNmm/s.
 19. An article of manufacture havingat least one component thereof fabricated from the composition ofclaim
 1. 20. The article of claim 19, wherein the composition furthercomprises at least one additive selected from the group consisting ofprocess oils, fillers and blowing agents.
 21. The article of claim 20,wherein the process oil is present in an amount within a range of fromgreater than 0 to about 50 percent by weight, based on total compositionweight.
 22. The article of claim 20, wherein the filler is selected fromthe group consisting of glass, silica, carbon black, metal carbonates,metal sulfates, talc, clay and graphite fibers.
 23. The article of claim20, wherein the filler is present in an amount within a range of fromgreater than 0 to about 70 percent by weight, based on total compositionweight.
 24. The article of claim 20, wherein the blowing agent ispresent in an amount within a range of from greater than 0 to about 10percent by weight, based on total composition weight.
 25. The process ofclaim 14 or claim 15, wherein a sequential step c) follows b), and stepc) comprises converting the rheology modified polymer blend into anarticle of manufacture.
 26. The process of claim 25 further comprisingsequential intermediate steps b1) and b2) that precede step c), step b1)comprising recovery of the rheology modified polymer blend as a solidand step b2) comprising conversion of the solid to a melt statesufficient for fabricating the article of manufacture.